Design a Dropbox-like file sync service

Q: Design a Dropbox-like file sync service

This question evaluates a candidate's ability to design large-scale distributed file storage and synchronization systems, testing competencies in data modeling, consistency and conflict resolution, chunking/delta sync, durability, security, and operational concerns like observability and disaster recovery.

Q: How do I approach System Design interview questions?

System Design questions require understanding of core concepts and practice. PracHub provides solutions with explanations to help you master system design interviews.

Q: What difficulty level is this interview question?

This is a hard difficulty System Design question, commonly asked during Onsite rounds at Meta.

Q: What role is this question designed for?

This question is commonly asked for Software Engineer candidates at Meta during technical interviews.

Question

Design a Dropbox-like File Storage and Sync Service

You are asked to design a cross-device file storage and synchronization service at internet scale (hundreds of millions of users). The system must support multi-device sync, offline edits, and reliable sharing—with strong durability and clear consistency guarantees.

Functional Requirements

Multi-device sync across desktop and mobile
Offline edits with eventual synchronization
Conflict detection and resolution
Large file support with chunking and delta sync
Deduplication and compression
Versioning and restore
Sharing with ACLs (users, groups, link sharing)
Near real-time notifications
Quota and billing support

Non-Functional Requirements

Scale to hundreds of millions of users and billions of files
High durability and availability across regions
Clear consistency model for metadata and content
Mobile constraints (battery, background limits, metered networks)
Encryption options: client-side (E2EE) and server-side
Observability: metrics, logs, tracing, integrity checks
Disaster recovery with defined RPO/RTO

Deliverables

Provide:

High-level architecture: clients and sync engine, metadata service, blob storage/CDN
Data model: files, chunks, versions, tombstones, ACLs, journals
Read and write flows (including conflict and delta sync)
Consistency model and guarantees
Strategies for hotspots, backfills, and migrations
Notes on mobile constraints, encryption options, quota/billing, observability, and disaster recovery

Design a Dropbox-like file sync service

Quick Overview

Design a Dropbox-like File Storage and Sync Service

Functional Requirements

Non-Functional Requirements

Deliverables

Solution

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